Method of distributing liquid in apertured absorbent pads

ABSTRACT

This invention relates to absorbent pads, and methods for fabricating absorbent pads, having improved fluid intake and preferential wicking in the longitudinal direction. The absorbent pads have patterns of apertures which encourage the preferential wicking. The apertures are characterized by size, spacing from each other, and depth of penetration into the absorbent pad, such that fluid intake rate is increased and distribution of fluid in the longitudinal direction is improved. Apertures are preferably spaced close enough to each other that aqueous liquid is preferentially transferred from aperture to aperture by capillary effect, along the length of the absorbent pad. Preferential wicking between apertures in the longitudinal direction increases the overall effective liquid absorption rate of the absorbent pad, thereby increasing overall effective liquid capacity of the respective absorbent article. A novel method of fabricating an absorbent pad of the invention includes penetrating into but not through the absorbent pad using heated pin elements. The heated pin elements fork a plurality of apertures in a first surface of the pad, the pad having higher density proximate the apertures than the overall density of the absorbent pad. The lower density areas of the-pad have greater aqueous intake rates than higher density portions of the absorbent pad.

This application is a divisional of Ser. No. 08/813,934 filed Mar. 10,1997.

FIELD OF THE INVENTION

The present invention relates to apertured pads for use in absorbentarticles. More particularly, the invention relates to patterns ofapertures, sizes of the apertures, depths of the apertures, and otheraspects of apertured absorbent pads that improve both the intake ratefor receiving aqueous fluid thereinto, movement of the liquid within theabsorbent pad, and the overall effective ability of the pad to receivethe liquid and move the liquid along the length of the absorbent pad.

BACKGROUND OF THE INVENTION

Absorbent pads are well known for use in absorbent articles. Absorbentpads may be located e.g. between the bodyside liner and the outer coverof an absorbent article. Absorbent pads receive and retain liquid fromthe body of a user. The absorbent pad must be effective to receive, fromthe body of the user, and to retain, a sufficient quantity of liquid toprevent leaking of the liquid from the absorbent article.

It is known to use apertures in absorbent articles to help channelliquids away from the body of the wearer and into the absorbent materialof the absorbent article. In conventional such use, a liner sheet of theabsorbent pad is bonded to an absorbent body of the absorbent pad. Insome such conventional embodiments, apertures extend through theabsorbent body, and the liner sheet extends through the aperture and isbonded to the backing sheet or a bonding sheet on the opposite side ofthe absorbent pad.

There is also known a quilted diaper having apertures extending entirelythrough the absorbent pad. An inner sheet is secured to a back sheet inthe apertures. An intervening layer having smaller apertures may belocated between the inner sheet and the absorbent pad.

It is also known to have a disposable insert for a diaper wherein theinsert has an impermeable, but slitted, top sheet. The slits extendentirely through the top sheet, and may open and allow liquid to passthrough, thereby to enter an underlying absorbent pad until the pad issaturated. As liquid is received into the absorbent pad, dimples in theabsorbent pad expand, and close the slits, permitting substantially noentry or exit of liquid from the absorbent pad after the absorbent padbecomes saturated with the liquid.

SUMMARY OF THE DISCLOSURE

This invention relates to absorbent pads, especially absorbent pads usedfor absorbing body exudates, and methods for fabricating such absorbentpads, having improved fluid intake rates, and preferential wicking alongthe longitudinal dimension of the pad. The absorbent pads have patternsof apertures which encourage the preferential wicking. The apertures arecharacterized by size, spacing from each other, and depth of penetrationinto the absorbent pad, as well as increased density of fibrous materialof the pad about and proximate the surfaces of the apertures, such thatfluid intake rate is increased and distribution of fluid in thelongitudinal direction is improved, over rates and distribution ofconventional pads.

Apertures are preferably spaced sufficiently close to each other thataqueous liquid is transferred from aperture to aperture by capillaryeffect. Spacing and arrangement of the apertures in the aperture arrayis such as to facilitate traverse of liquid, being absorbed into the padand transferred within the pad, along the length of the absorbent pad,rather than across the width of the pad. Preferential wicking betweenapertures in the longitudinal direction increases the overall effectiveliquid absorption rate of the absorbent pad, because absorbed liquid israpidly transported away from the locus of absorption, thus voidingspace at the locus of absorption, which voided space can be used forrapidly absorbing additional quantities of liquid. The perceived valueof the invention is in thus increasing the overall effective capacity ofthe absorbent article to absorb liquid over a relatively short timeperiod representative of conditions of use in absorbing body exudates.

A novel method of fabricating an absorbent pad of the invention includespenetrating into but generally not through the absorbent pad, usingheated pin elements. The heated pin elements form a plurality ofapertures in a first surface of the pad. The pad has higher densityproximate the apertures than the overall density of the absorbent pad.The lower density areas of the pad have greater aqueous intake ratesthan higher density portions of the absorbent pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a first embodiment of an absorbent pad of theinvention.

FIG. 2 shows a cross-section of the absorbent pad taken at 2--2 in FIG.1.

FIG. 3 shows a fragmentary cross-section of apparatus for formingapertures in the absorbent pad according to the invention.

FIG. 4 shows a pictorial view of a first, flat-nosed tip of a pinelement for use in the apparatus of FIG. 3.

FIG. 5 shows a pictorial view of a second pin element, having an axiallyinwardly disposed cavity at the tip of the pin element.

FIG. 6 shows a representative top view of an absorbent article includingan absorbent pad of the invention.

FIG. 7 shows a cross-section of the absorbent article, taken at 7--7 inFIG. 6.

FIG. 8 shows a top view of an absorbent pad that did not function aswell as desired.

FIG. 9 shows a top view of another absorbent pad of the invention.

FIG. 10 is a graph showing comparative wicking distance as a function ofaperture size and arrangement.

FIG. 11 is a graph showing comparative intake time as a function ofaperture size and arrangement.

The invention is not limited in its application to the details of theconstruction and the arrangement of the components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments or of being practiced or carried out invarious ways. Also, it is to be understood that the terminology andphraseology employed herein is for purpose of description andillustration and should not be regarded as limiting. Like referencenumerals are used to indicate like components. Further, the abovedrawings are not drawn to scale and do not so limit the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention is directed toward an absorbent article havingincreased fluid intake rate and improved distribution of fluid. Theinvention includes an absorbent pad having a number of aperturesarranged in a pattern to promote wicking in the longitudinal direction.The number of apertures, the surface area of the apertures, and thedepths of the apertures, all contribute, in combination, to the improvedwicking effect, and distribution, of liquid. Another benefit of theinvention is that the apertures improve the structural integrity of theabsorbent pad.

Throughout the disclosure and claims, the phrase "absorbent article"means infant care, adult care and feminine care products which absorbfluids from the body of the user.

Throughout the disclosure and claims, the word "fluid" means flowableelements of urine, feces containing liquid, menses, and any other bodilyfluid that can be transferred from a user to an absorbent article.

The terms "densification" and/or "densified" defines portions of anabsorbent pad which have a higher density of fibrous material, such ascellulosic fluff, than the overall average density of the respectiveabsorbent pad. Such densification does, however, leave sufficient openspace in the matrix of fibers to readily receive aqueous liquidsthereinto in absorbing liquids into pad 10.

FIGS. 1 and 2 illustrate a first absorbent pad 10 of the invention.Absorbent pad 10 includes a first apertured surface 12, and a secondopposing reference surface 14. Absorbent pad 10 has a length "L," awidth "W," shown in FIG. 1, and a thickness "T," shown in FIG. 2. Secondreference surface 14 preferably has no apertures, or few apertures.Absorbent pad 10 has a longitudinal axis 16 extending along the lengththereof. A multiplicity of apertures 20 extend from first surface 12inwardly into the absorbent pad toward second reference surface 14, andgenerally terminate as blind apertures at respective bottoms 24.Apertures 20 are typically formed, in a nip, by heated pin elements.

The absorbent pad material around apertures 20 is more dense thanportions of absorbent pad 10 which are spaced from the apertures. Suchdenser zones about apertures 20 encourage wicking of fluid into thedenser zones. Preferred embodiments have aperture patterns whichpreferentially wick fluid longitudinally along the length of absorbentpad 10 and away from the center thereof. Thus apertures 20 improve theoverall distribution of fluid in absorbent pad 10. Surprisingly, thenumber of apertures, spacing of apertures, and the arrangement of theapertures in the aperture array can also improve the intake rate ofabsorbent pad 10. Therefore, the intake rate and the pattern ofdistribution of liquid within the absorbent pad 10 is improved in theinvention.

Exemplary apertures 20 shown in FIG. 1 are rectangular. Such rectangularapertures can have a length of up to about 1 inch and a width of up toabout 1/4 inch. As illustrated in FIG. 1, some or all of the aperturescan have smaller sizes. Indeed, in some embodiments of the invention,all the apertures have substantially the same size, both cross-sectionaldimensions and depths. However, aperture cross-sections and aperturedepths can differ for different apertures in the same absorbent pad.

As shown in FIG. 1, the lengths of rectangular apertures 20 extend alongthe length "L" of absorbent pad 10.

In preferred embodiments, substantially none of apertures 20 extendthrough absorbent pad 10 and thus penetrate surface 14. As shown in FIG.2, apertures 20 generally extend from first surface 12 inwardly of theabsorbent pad for about 90% of the dimension of thickness "T" ofabsorbent pad 10. As shown in FIG. 2, each aperture 20 has an inneraperture surface 22 extending from first surface 12 toward bottom 24,and including the perimeter sidewalls 25 on the interior of theaperture. During manufacture or during later handling, some or all ofbottoms 24 may rupture as shown at 27 in FIG. 2, such that therespective aperture extends in principle entirely through absorbent pad10. Generally, however, bottoms 24 are closed as shown at the aperturesillustrated on the left side of FIG. 2. However, even where the bottomis ruptured as at 27, the size of the open area of the opening socreated is small by comparison to the open cross-sectional area (topview) of the main body of the respective aperture 20. In any event,ruptures 27 represent bottoms 24 in which openings have been created,and wherein bottoms 24 generally remain intact, though ruptured.

Absorbent pad 10 suitably comprises a matrix of hydrophilic fibers, suchas a web of cellulosic fluff. Optionally, a high-absorbency materialcommonly known as superabsorbent material can be included in absorbentpad 10. In a particular embodiment, absorbent pad 10 can include amixture of superabsorbent hydrogel-forming particles and wood pulpfluff. Although cellulosic fluff is preferred, one may use syntheticfibers, polymeric fibers, meltblown fibers or a combination of meltblownfibers and natural fibers. Superabsorbent material may be substantiallyhomogeneously mixed with the hydrophilic fibers, or may be otherwisecombined into absorbent pad 10.

Absorbent pad 10 may comprise a laminate of fibrous webs andsuperabsorbent material or other suitable means of maintaining asuperabsorbent material in a localized area.

Absorbent pad 10 may have any of a number of shapes. For example, andwithout limitation, absorbent pad 10 may be rectangular, I-shaped orT-shaped.

The high-absorbency material in absorbent pad 10 can be selected fromamong natural, synthetic and modified natural polymers and materials.The high absorbency materials can be inorganic materials, such as silicagels, or organic compounds, such as crosslinked polymers. The termcrosslinked refers to any means for effectively rendering normallywater-soluble materials substantially water insoluble but swellable,whereby absorbent properties are available but the swelled material issubstantially immobile after absorbing water-based liquids. Such meanscan include, for example, physical entanglement, crystalline domains,covalent bonds, ionic complexes and associations, hydrophilicassociations such as hydrogen bonding, and hydrophobic associations orVan der Waals forces.

Absorbent pad 10 can include a standard barrier tissue layer 29 coveringfirst surface 12 and a forming tissue layer 31 covering second referencesurface 14 of the absorbent pad. Such tissue layers are well known inthe art both in terms of materials and functions. The tissue layersgenerally are permeable to fluids, but retain material of absorbent pad10 therein. In adult care products, however, a single tissue layer canbe wrapped entirely about, and secured to, absorbent pad 10. Otherarrangements, containing layers of various materials disposed onsurfaces 12, 14, and/or encompassing absorbent pad 10, are contemplatedas being within the scope of the invention.

As shown in FIG. 2, inner aperture surface 22 of an aperture 20,comprehends the entirety of the surface of the pad disposed insideopening 33 of the aperture. Thus, inner aperture surface 22 includes therespective bottom 24 as well as sidewalls 25. The density of theabsorbent pad proximate inner aperture surface 22 is greater than theoverall average density of the absorbent pad. Such higher density thusgenerally extends along the entire depth of side walls 25 as well asacross bottom 24. Such increase in density is generally accompanied bycorresponding increased overall structural integrity of absorbent pad10, whereby structural integrity of absorbent pad 10 is more readilymaintained during use of the absorbent pad.

In operation, when an insult of a liquid, such as urine, is poured ontothe center of first surface 12 of absorbent pad 10, apertures 20 assistin distributing the urine along the length "L" of the absorbent padwhich extends along longitudinal axis 16. First, the free-flowing liquidis received within the void volume inside respective apertures. Second,the denser zones surrounding the apertures, including side walls 25 andbottoms 24, transport the liquid more efficiently than zones of averagedensity. Third, zones of intermediate density between apertures arrayedalong length "L," also urge movement of the liquid in a longitudinaldirection along length "L" and away from the locus of the insult.Fourth, lower density zones, spaced farther from the denser zones thanthe zones of intermediate density, absorb the liquid at a higherabsorption rate than zones of higher density. Thus the distribution ofurine or other exudate in both frontward and rearward longitudinaldirections along longitudinal axis 16 is improved by apertures 20 as inFIG. 1.

Absorbent pad 10 of FIG. 1 has an exemplary length of about 21 inches,an exemplary width of about 5.5 inches, and an exemplary thickness "T"of about 1/4 inch. This size pad is preferred in adult care products.Other absorbent pads 10, having smaller sizes, are generally preferredfor infant care and feminine care products, and are also within thescope of the invention, as are larger size absorbent pads.

In preferred embodiments, the invention contemplates at least 40 ofapertures 20 to provide the proper wicking effect without having anadverse consequence on fluid intake. Most embodiments preferably have atleast 80 apertures. The large number of apertures provides morelocations of increased density located at first surface 12 of absorbentpad 10. The large number of locations improves distribution e.g. wickingof fluid from aperture to aperture. Some embodiments include 120 or moreapertures. However, if the number of apertures becomes to large, thecorresponding aperture size may be so small that the beneficial effectsof the invention are not achieved.

Individual apertures 20 each have a cross-sectional area, across theopen cross-sectional area between sidewalls 25 of the respectiveaperture. Such cross-sectional area is defined transverse to animaginary axis extending through the absorbent pad 10, e.g.perpendicular to surface 12. The open cross-sectional area typically isfrom about 0.0025 square inch to about 0.25 square inch. For apertureshaving a smaller cross-sectional area, the impact on distribution andfluid intake is not significant.

The relationship between the cross-sectional area of apertures 20 andthe total surface area of first surface 12 is also an important featureof the invention. The sum of the open cross-sectional areas of apertures20 should be in a range of from about 5% to about 40% of the totalsurface area of first surface 12 of absorbent pad 10. For betterresults, the open cross-sectional area most preferably comprises fromabout 11% to about 32% of the total surface area of first surface 12.

In FIG. 1, the ratio of the length of individual apertures 20 withrespect to length "L" of absorbent pad 10 along longitudinal axis 16 isabout 1:20. The invention contemplates the ratio of the length ofindividual apertures 20 with respect to length "L" being from about 1:10to about 1:250. The length of a circular aperture 20 can be deduced byutilizing the diameter of the aperture.

While FIG. 2 shows apertures 20 having depths equal to about 90%, ofthickness "T," depths from about 40% to about 99% of the thickness arepermissible with preferred depths being at least 50%, most preferably atleast 60%. Further, some apertures 20 can penetrate through bottom 24 ofabsorbent pad 10 without destroying utility of the pad. Such penetrationgenerally comprises an opening in bottom 24, as at rupture 27, which issmaller, typically substantially smaller, in cross-section than thegeneral open area cross-section defined by the respective aperture 20.

FIG. 1 shows a multiple serpentine pattern for rectangular apertures 20in first surface 12 of absorbent pad 10. As will be shown by theexamples later, the arrangement of apertures 20 with respect to eachother has a profound effect on the distribution of fluid in thelongitudinal direction of absorbent pad 10. Further, and surprisingly,the arrangement of apertures with respect to each other can actuallyincrease the fluid intake rate of the absorbent pad over a reasonablyshort test period.

The general nature of apparatus useful for forming apertures 20 inabsorbent pads 10, or a continuous absorbent core passing through a nip,is disclosed in U.S. Pat. No. 4,886,632 to Van Iten et al which ishereby incorporated by reference in its entirety. Van Iten et aldisclose apparatus for forming apertures of generally uniform opencross-section through the entirety of the thickness of a web. Theinvention herein utilizes the apparatus of Van Iten et al, withmodifications to apparatus and methods of use as discussed hereinafter,to form generally closed-bottom apertures in absorbent pads 10 havingmuch greater thicknesses than the webs of Van Iten et al. U.S. Pat. No.5,188,625 to Van Iten et al, hereby incorporated by reference in itsentirety, discloses using a similar apparatus to form apertures througha liquid-permeable cover layer..

FIG. 3 shows a cross-sectional view of absorbent pad 10 directed througha nip defined by a first member including pin element 26 and a secondmember including strip 28 and sleeve 30. Pin element 26 has a roundedtip 32, as shown. Rounded tip 32 tends to form a rounded bottom 24 tothe aperture so formed, without completely penetrating the thickness "T"of absorbent pad 10. Heating units (not shown) heat respective pinelements 26 and sleeve 30. Strip 28 and sleeve 30 comprise heatconducting material, such as brass, steel or aluminum. Pin elements 26also comprise heat conducting material, such as brass or steel.

In operation, as absorbent pad 10 moves through the nip, respectiveheated pin elements 26 of the first member enter heated strip 28,penetrating openings 34. The force of pin elements 26 rotating throughthe nip pushes respective elements of absorbent pad 10 into openings 34of strip 28, thus forming apertures 20 in the absorbent pad. The heatingof pin elements 26 and strip 28, including outer walls of openings 34,in combination with force exerted at the nip, in absorbent pad 10,softens the fibers while the respective collection of fibers is beingacted on by pin element 26. The fibers are thus compressed togetherwhile in the heated condition, both at tip 32 and along side walls 34,squeezing the pad between pin element 26 and side walls 25, and betweenpin element 26 and second surface 14.

While FIGS. 12 and 13 of Van Iten et al '632 show a shoulder on the pinelement forming an enlarged area of high density material at the surfaceof the sheet being processed, this enlarged area can be reduced bytapering the shoulder of the pin element as shown in FIG. 3. The pinelement of Van Iten et al breaks the sheet of material being worked. Bycontrast, in applicants' FIG. 3, the pin element breaks few, if any,fibers, and forces a portion of applicants' thicker absorbent pad 10into opening 34 where densification is effected.

Preferred temperatures of strip 28 and pin elements 26 are equal to orgreater than 300 degress F. up to about 500 degress F. The temperatureand pressure, in combination, at the nip cause densification ofabsorbent pad 10 proximate and about apertures 20 so formed by thecombination of softening, and simultaneously compressing, the materialof the absorbent pad. The heating tends to soften, melt and/or bondfibers of absorbent pad 10 in the compressed dense state shown in FIG.3. Thus, after the materials of absorbent pad 10 have passed throughapparatus 35 of FIG. 3, the combination of compression and heatingcauses the pad material adjacent apertures 20 to permanently retain itscompressed characteristic and corresponding high density, proximate theentirety of aperture surface 22, including side walls and bottoms of therespective apertures. By contrast, the sharp tip of the pin element ofVan Iten et al penetrates entirely through the thinner web material,whereby the apertures serve more as conduits for drainage than asreservoirs for containment as in the instant invention.

Pin elements 26 and strip 28 can be cooperatively configured to provideslotted, but still blind, apertures as shown in FIG. 1. By "blind," wemean that the aperture is open on only one end, for example, the end atsurface 12.

Other configurations and arrangements of pin elements 26 and cooperatingopenings 34 are within the scope of the invention. For example, FIG. 4shows a pin element 26 having a flat end at tip 36. Tip 36 is preferablyreasonably chamfered, whereby tip 36 generally creates apertures 20without complete penetration of absorbent pad 10.

FIG. 5 shows a pin element 26 having a recessed end 38 at the tip,including a rim 37, and a cavity 39 extending, from rim 37, axially andtransversely inwardly into the end. In usage with apparatus 35 of FIG.3, the tip having the recessed end forms a pillow of partially densifiedmaterial in the bottoms of the respective apertures. The density of thepillow so produced is greater than the overall density of absorbent pad10 and less than the high density pad material at rim 37. Other shapes,such as star shapes, diamond shapes and triangle shapes or otherornamental and/or utilitarian designs can be utilized for pin elements26.

Pin element diameter, pin element shape, pin element/strip temperature,pin element pattern, nip gap and nip pressure are among the variableswhich can be controlled in forming absorbent pad 10. These variables canvary the density and pattern of apertures 20 and thus the overallperformance of absorbent pad 10. For example, in some embodiments, pinelements 26 need not be heated.

Referring to FIG. 3, the open aperture/space between the side wall ofpin element 26 and side wall 34 of the opening is sized in cooperationwith the thickness and strength of the web/pad to be worked, and pinelement 26 is configured to be sufficiently blunt thatsurface-to-surface complete penetration is avoided such that pin element26 pushes on the pad material at surface 12, pushing the pad materialahead of it, into the opening in strip 28, with correspondingcompression and densification of pad material to thereby make a blind,closed-end, aperture in the pad material, with the open end of theaperture opening at surface 12. FIG. 3 illustrates only one such pinelement forming only one aperture. Many such pin elements and stripopenings can, of course, be used on cooperating registered nip rolls toform such apertured product at production line speeds. Pin element 26can be pointed, but sufficiently spaced from sleeve 30, to avoidcomplete penetration of the web/pad being worked.

FIGS. 6 and 7 illustrate absorbent pad 10 incorporated into an absorbentarticle 40. Absorbent article 40 includes absorbent pad 10, bodysideliner 42, outer cover 44, and attachment ears 46. Bodyside liner 42 isgenerally in surface-to-surface relationship with first surface 12 ofabsorbent pad 10. Outer cover 44 is generally in surface-to-surfacerelationship with second surface 14 of absorbent pad 10. The respectiveelements shown in FIG. 7 can be secured to each other by ultrasonicbonding, adhesives, or other methods well known in the art.

FIG. 6 shows a serpentine pattern of apertures 20 extending along thelength of pad 10. Four rows of apertures 20 are shown, each extendingalong a serpentine path. The pattern of apertures 20 shown in FIG. 6thus resembles four alternating sine waves. Adjacent paths of apertures20 alternate between repeating maximum distances "MXW" and repeatingminimum distances "MW" between successive apertures in the respectiveadjacent paths.

Absorbent article 40 in FIG. 6 is applied to the body of a user bysecuring attachment ears 46 in a rear portion of the absorbent articleto a securement surface element (not shown) on outer cover 44 of thefront portion. Attachment ears 46 can, for example, comprise the hooksof a hook and loop fastening system. The securement surface elementtypically comprises a corresponding loop material attached to outercover 44 in the front portion of absorbent article 40 and adapted toreleasably engage with the hook material. Other well known fasteningdevices can also be used to support absorbent article 40 on the user.For example, a cohesive system, an adhesive fastener system, belts orthe like may also be utilized to secure absorbent article 40 to the bodyof the user.

A suitable bodyside liner 42 may be manufactured from a wide selectionof web materials, such as porous foams, reticulated foams, aperturedplastic films or natural fibers. For example, bodyside liner 42 maycomprise wood or cotton fibers. Other possible materials are syntheticfibers, such as polyester or polypropylene fibers, or a combination ofnatural and synthetic fibers. Bodyside liner 42 is suitably utilized tohelp isolate the liquids held in absorbent pad 10 from the skin of auser.

Various woven and nonwoven fabrics may be used for bodyside liner 42.For example, bodyside liner 42 may be composed of a meltblown orspunbonded web of polyolefin fibers. Bodyside liner 42 may also comprisea carded and/or bonded web composed of natural and/or synthetic fibers.Bodyside liner 42 may also be composed of a substantially hydrophobicmaterial wherein the hydrophobic material is treated with a surfactantor otherwise processed to impart a desired level of wettability andhydrophilicity.

In a particular embodiment of the present invention, bodyside liner 42may comprise a nonwoven, spunbonded, polypropylene fabric composed ofabout 2.8-3.2 denier fibers formed into a web having a basis weight ofabout 22 grams per square meter and a density of about 0.06 grams percubic centimeter. The fabric is then surface treated with about 0.3weight percent of a surfactant. Bodyside liner 42 may comprise amultiplicity of components or layers which correspond to any of thematerials disclosed herein, as well as others known in the art.

Since the web material from which bodyside liner 42 is made has anoverall pattern of generally uniform pores, the liner itself ispreferably free from larger size apertures or slits formed after thebodyside liner material has been fabricated. Apertures having a diameterof more than about 0.1 inch or slits having a length of more than about0.25 inch, in the bodyside liner, are not contemplated as beingdesirable for the disclosed invention. Further, bodyside liner 42 mostpreferably comprises a web of material, permeable to liquid, and havingno apertures or slits of meaningful size or length formed therein.

It is generally preferred that outer cover 44 of absorbent article 40 beformed from a material which is substantially impermeable to liquids. Atypical outer cover 44 may be manufactured from a thin plastic film orother flexible liquid-impermeable material. For example, outer cover 44may be formed from a polyethylene film having a thickness of from about0.012 millimeters to about 0.051 millimeters. If outer cover 44 shouldhave a more clothlike feeling, it may comprise a polyethylene filmlaminated to a surface of a nonwoven web, such as a spunbonded web ofpolyolefin fibers. For example, a polyethylene film having a thicknessof about 0.015 millimeters may have thermally or otherwise laminatedthereto a spunbond web of polyolefin fibers having a thickness of from1.5 to 2.5 denier per filament, which nonwoven web has a basis weight ofabout 24 grams per square meter. Further, outer cover 44 may be formedof a woven or nonwoven fibrous web which has been totally or partiallyconstructed or treated to impart a desired level of liquidimpermeability to selected regions that are adjacent or proximateabsorbent pad 10. Still further, outer cover 44 may optionally becomposed of a microporous material which permits vapors to escape fromthe absorbent pad 10 and through outer cover 44 while preventing liquidexudates from passing through the outer cover 44.

An optional surge layer (not shown) can be located between and insurface-to-surface contact with first surface 12 of absorbent pad 10and/or bodyside liner 42. The surge layer can comprise materials setforth in U.S. Pat. No. 5,486,166 to C. Ellis and D. Bishop, entitled,"Fibrous Nonwoven Web Surge Layer for Personal Care Absorbent Articlesand the Like"; and U.S. Pat. No. 5,490,846 to C. Ellis and R. Everett,entitled, "Improved Surge Management Fibrous Nonwoven Web for PersonalCare Absorbent Articles and the Like", the disclosures of which areherein incorporated by reference. Further, other surge layer materialsknown in the art can also be utilized.

During construction of absorbent article 40, absorbent pad 10 ispositioned between outer cover 44 and bodyside liner 42. Bodyside liner42 and outer cover 44 are then secured to one another, with absorbentpad 10 therebetween. Optionally, absorbent pad 10 can be secured toouter cover 44 and/or bodyside liner 42. Securement can be effected byadhesives, ultrasonic bonding, stitching or any other well known methodof forming an absorbent article. Bodyside liner 42 does not extendsubstantially into apertures 20 of absorbent pad 10, and specificallydoes not generally follow side wall 25. Rather, bodyside liner 42 isspaced from bottom 24 and generally from side wall 25.

When absorbent article 40 is mounted on the body of a user, fluid, suchas urine, which contacts absorbent pad 10 flows preferentially along thelongitudinal direction of the pad and is absorbed into the aperturedpad. The serpentine pattern, and relative spacing of apertures 20 fromeach other, as in FIG. 6, assist in drawing fluid in the longitudinaldirection along first surface 12 and from within absorbent pad 10 andapertures 20.

One theory of how absorbent article 40 operates includes a first one ofapertures 20 initially receiving liquid. After substantial passage ofliquid through bodyside liner 42 and into first aperture 20, the liquidis drawn by capillary effect to a second aperture 20, closely adjacentthe first aperture. The apertures of the serpentine pattern are locatedclose enough to one another to generally promote wicking of fluid in thelongitudinal direction, by preferentially passing liquid from the oneaperture to the second aperture by a capillary effect. Thus, by usingcapillary effect, as well as other transport properties, fluid can bedrawn from the first aperture to the second aperture. The effect can berepeated for other relatively closely spaced apertures along a given(serpentine) path to provide a flow in the longitudinal direction. Thepattern of apertures 20 thus provides a path for enhanced wicking anddistributing fluid in the longitudinal direction.

As shown in FIG. 6, the apertures in a given serpentine path can bespaced from each other by a distance approximately equal to the diameterof an individual aperture. By so spacing the apertures using e.g. pinelements 26 in forming the apertures, the pad material bridging betweensuch closely adjacent apertures is partially densified/compressed, thusto encourage fluid to flow along the path of apertures in the directionof longitudinal axis 16, along the length of absorbent pad 10, inpreference to flow transverse to axis 16.

Another theory regarding the effect of absorbent pad 10 of absorbentarticle 40 can be expressed as considering density at locations of theabsorbent pad. Densified apertures 20 of absorbent pad 10 have a higherdensity than locations on first surface 12 of the absorbent pad spacedaway from the apertures. As described earlier, the density differencesare caused by apparatus 35 of FIG. 3 utilizing heated pin elements 26 toform apertures 20.

Further, in theory, first surface areas of absorbent pad 10 up to afirst distance "D" from apertures 20 have a higher density than areas ofthe absorbent pad at locations on the first surface a greater distancethan "D" away from the apertures. This is believed to be caused, atleast in part, by compression of absorbent pad 10 at first surface 12caused by physical formation of apertures 20. Thus, besides formingapertures 20 having higher density material, apparatus 35 shown in FIG.3 draws material of pad 10 toward the several apertures, thereby alsoincreasing the density of absorbent pad 10 at first surface 12 up todistance "D" about each aperture. Therefore, the wicking effect of fluidis increased within the area of absorbent pad 10 which is within thefirst distance "D" from the respective aperture 20.

In practical terms, the pattern of apertures 20 is preferably arrangedsuch that at least a second aperture 20 is within the first distance "D"from each aperture. Typically second and third apertures are generallyarranged at surface 12 on opposing sides of each aperture, thus todefine a given one of the serpentine or other paths/lines of apertures,and thus defining a distribution line transporting liquid preferentiallylongitudinally from the locus of application of the insult. Thisarrangement increases and promotes wicking of fluid from aperture toaperture. Apertures 20 are generally aligned and spaced in thelongitudinal direction to promote distribution of fluid in thelongitudinal direction, thereby obtaining use of a greater portion ofthe first surface 12 of absorbent pad 10 to receive and retain suddeninfluxes of relatively larger quantities (e.g. body exudate quantities)of fluid.

While the first distance "D" has not been specifically calculated, theinvention contemplates that the gradient of the density of material ofabsorbent pad 10 decreases as the distance increases away from one ofapertures 20. Thus the first distance really describes the distance atwhich the density of absorbent pad 10 at first surface 12 decreasessufficiently to prevent the preferred passage or spreading of fluid tothe next one of apertures 20 by capillary effect or the like. Thedensity of material at and adjacent first surface 12 of absorbent pad 10can continue to decrease as a gradient beyond the first distance fromone of apertures 20. The first distance "D" can comprise at least thediameter of an individual one of apertures 20, and may comprise agreater distance. At least one and preferably two apertures 20 alignedin the longitudinal direction are arranged within the first distance ofone of the apertures such that fluid is directed from the first one ofthe apertures along and proximate the first surface of absorbent pad 10to the other nearby apertures.

While the above theories of operation attempt to explain how improvedfluid intake and distribution are obtained, applicants choose to not bebound by any particular theory described above. The test resultsdescribed below illustrate the surprising advantage gained by theinvention.

TEST PROCEDURE

Tests were conducted using a fluid intake flowback evaluation (FIFE)tester (not shown). The FIFE tester has two PLEXIGLASS plates. The topplate of the FIFE tester includes a cylinder having an inner diameter of2 inches. The top plate has a circular hole formed in the centerthereof. The cylinder extends upwardly substantially perpendicular tothe surface of the top plate. The cylinder fits within the circular holeand is secured therein by an adhesive. The adhesive permanently securesthe cylinder as an integral part of the top plate and prevents liquidfrom leaking outwardly onto the top surface of the top plate. Pinelements are located near outside corners of the bottom plate. The pinelements align with apertures in the top plate to mount the platestogether. A funnel is placed at the top of the cylinder to pour liquidinto the test device. The combined mass of the top plate of the FIFEtester including the cylinder, and the funnel is from 900 to 1100 grams.

The test products comprised absorbent pads from DEPEND Extra AbsorbencyElastic Leg Undergarments. Absorbent pads 10 had a length of 21 inches,a width of 5.5 inches and a thickness of about 0.25 inch. For purpose ofthe test, the elastics were removed.

In use, a DEPENDS absorbent article 40, including a bodyside liner 42,an outer cover 44, and absorbent pad, was placed with bodyside liner 42in surface-to-surface relationship with the top plate of the FIFEtester. Outer cover 44 of absorbent article 40 was in surface-to-surfacerelationship with the bottom plate of the FIFE tester. Thus absorbentarticle 40 was located between the top plate and the bottom plate. Inuse, the bottom plate and top plate of the FIFE tester both definesubstantially horizontal planes.

Absorbent pad 10 was centered such that the cylinder of the top plate ofthe FIFE tester was above the center of the absorbent pad and in contactwith the bodyside liner. The test began with a first insult of 80milliliters of saline solution being poured rapidly into the testcylinder via a funnel placed atop the cylinder. Time was recorded fromfirst contact of solution to the absorbent article until completeabsorption had occurred (intake time in seconds). Immediately after theliquid was completely absorbed, the length of the pad over which liquidwas distributed was measured, thus giving a wicking distance. The liquidwas colored to facilitate detection of wicking distance. Thismeasurement was taken from the edges of the colored material on theextreme left point to the extreme right point of the liquid stain alonglongitudinal axis 48 of absorbent article 40. After a five minute wait,a second 80 milliliter insult was poured into the FIFE cylinder. Thetime and distance were recorded as for the first insult. A third andfinal insult of 80 milliliters was applied after another 5 minute delay,and the intake and wicking values were recorded. A final 5 minute delaywas added to compare the effects of wicking over time. Only the distancemeasurement of wicking was taken after the last 5 minute delay.

TEST RESULTS

FIGS. 8 and 9 show patterns of apertures used to generate test results.FIG. 8 shows a solid pattern (A) of apertures 20 having diameters of0.109 inch. FIG. 9 shows a solid pattern (B) of apertures 20 havingdiameters of 0.25 inch. FIG. 6 shows an absorbent article 40 includingabsorbent pad 10 having a serpentine pattern (C) of apertures 20 whichgained the best overall test results. An absorbent pad was tested havingno apertures to use as a control for the other experiments. Results arelisted as follows. The wicking distance measured is inches in thelongitudinal direction between the leading edges of the colored materialon opposing sides of the colored material resulting from the insult,measured along the longitudinal axis 48 of the absorbent article. Thewicking distance is measured at the time the cylinder of fluid has beencompletely absorbed by the absorbent pad. The last measurement is taken5 minutes after the third insult of fluid has been absorbed by theabsorbent pad.

                  TABLE 1                                                         ______________________________________                                        WICKING DISTANCE SUMMARY -                                                                 FIRST    SECOND  THIRD   AFTER                                   PATTERN                                                                         INSULT     INSULT   INSULT  5 MINUTES                                       ______________________________________                                        Control  6.0 in.  7.7 in.    9.9 in.                                                                              12.4 in.                                  Pattern A                                                                              7.3 in.  10.2 in.  13.4 in.                                                                              16.1 in.                                  Pattern B                                                                              6.2 in.  9.0 in.   12.7 in.                                                                              15.9 in.                                  Pattern C                                                                              6.2 in.  9.8 in.   13.3 in.                                                                              16.8 in.                                  ______________________________________                                    

As shown by the above data, all of the patterns of higher densityapertures 20 have increased wicking in the longitudinal direction overthat of the Control, which had no apertures. The intake time for eachinsult equals the time required for the entire quantity of fluid in thetest cylinder to be absorbed by the absorbent pad. The intake timediffered greatly for the tested patterns as follows.

                  TABLE 2                                                         ______________________________________                                        INTAKE TIME SUMMARY                                                           PATTERN FIRST INSULT                                                                              SECOND INSULT                                                                              THIRD INSULT                                 ______________________________________                                        Control 27.8 sec.   57.5 sec.    57.3 sec.                                    Pattern A                                                                             40.1 sec.   61.1 sec.    80.1 sec.                                    Pattern B                                                                             14.2 sec.   32.2 sec.    33.4 sec.                                    Pattern C                                                                             11.0 sec.   31.0 sec.    31.4 sec                                     ______________________________________                                    

Pattern A comprised a full apertured pattern as shown in FIG. 8. About1600 apertures, each having a diameter of about 0.109 inch, are presentin Pattern (A). As shown in Table 2 above, the intake time for theabsorbent pad having pattern (A) of apertures 20 exceeded the intaketime of the Control absorbent pad. Thus, the embodiment of Pattern (A)is not suitable for use in an absorbent pad 10 where intake time is animportant consideration.

Pattern (B) is another fully apertured pattern as shown in FIG. 9. About660 apertures having a diameter of about 0.25 inch make up Pattern (B)of FIG. 9. Surprisingly, Pattern (B) had improved intake time comparedto both the Control absorbent pad and the Pattern (A) pad. It isinteresting to note that the improvement of Pattern (B) over Control,from the second insult to the third insult, remained at about 25seconds. This observation supports the theory that the open spacecross-section of the large apertures of Pattern (B) had an influence onthe intake time. Initially, the 14 seconds intake time improvement overthe Control absorbent pad could be attributed to the fluid filling voidscreated by the apertures faster than absorption could occur. The 25second improvement seen in the second insult resulted because thecontrol remained saturated while the open volume in the apertures ofpattern (B) was again open to retain fluid and because of improvedwicking of fluid. Thus the same improvement for the third insult waslikewise achieved.

Pattern (C) taken from absorbent article 40 of FIG. 6 provided the bestoverall results. The four serpentine patterns of Pattern (C) compriseabout 160 apertures, each having a diameter of about 0.25 inch. Theperformance of Pattern (C) was very good as the test results indicate.The intake time of Pattern (C) was better than the intake time forPattern (B). The longitudinal wicking distance for Pattern (C) was alsobetter than the wicking distance for Pattern (B) or any other testedpattern having an improved intake time. Thus Pattern (C) shown in FIG. 6provided highly desirable results for use in an absorbent article.

The Graphs of FIGS. 10 and 11 better show the relationship betweenintake time and wicking distance for the Control pattern and Patterns(A)-(C). In conclusion, the surface area of apertures, the number ofapertures, the depth of apertures, the density of pad material adjacentthe apertures, and especially the distance between apertures all areimportant factors in designing an improved absorbent pad for use inabsorbent articles.

Those skilled in the art will now see that certain modifications can bemade to the invention herein disclosed with respect to the illustratedembodiments, without departing from the spirit of the instant invention.And while the invention has been described above with respect to thepreferred embodiments, it will be understood that the invention isadapted to numerous rearrangements, modifications, and alterations, allsuch arrangements, modifications, and alterations are intended to bewithin the scope of the appended claims.

Having thus described the invention, what is claimed is:
 1. A method ofdistributing liquid in an absorbent pad, the method comprising the stepsof:(a) providing an absorbent pad comprising a fibrous material andhaving first and second opposing surfaces and a thickness therebetween,the first surface defining a total surface area, said absorbent padincluding at least first, second, and third apertures extending inwardlyfrom the first surface toward the second surface, said at least first,second, and third apertures forming a longitudinal pattern of aperturesalong the first surface, the second aperture being located between thefirst and third apertures, said absorbent pad comprising relativelyhigher density zones of fibrous material immediately proximate said atleast first, second, and third apertures, intermediate density zones offibrous material surrounding the higher density zones of said first,second, and third apertures, and relatively lower density zones of saidfibrous material outside said higher and intermediate density zones; (b)insulting said absorbent pad with aqueous liquid over a portion of thefirst surface, including over the first aperture, the portion of thefirst surface representing less than the total surface area; and (c)drawing portions of the insulting liquid from the first aperture intothe higher density zones of the absorbent pad and through saidintermediate density zones, toward the higher density zones of thesecond aperture,whereby the higher density zones immediately proximatethe first and second apertures, in combination with the intermediatedensity zones surrounding the higher density zones are spacedsufficiently close to form a liquid flow path for preferentially wickingand distributing the insulting liquid along the longitudinal pattern ofapertures on the first surface of the pad.
 2. A method as in claim 1,further comprising providing at least 40 apertures in the absorbent padin the longitudinal pattern, the apertures having higher density zonesof fibrous material proximate the apertures and intermediate densityzones of fibrous material surrounding the higher density zones andpreferentially wicking insulting liquid along the higher density zonesand intermediate density zones of the pad among ones of the at least 40apertures in the absorbent pad.
 3. A method as in claim 2, each aperturehaving a diameter and spaced from a respective aperture in thelongitudinal pattern a distance approximately equal to the diameter ofthe aperture so that the higher density and intermediate density zones,in combination, define said liquid flow path for preferentially wickingand distributing the insulting liquid along the pad in the longitudinaldirection.
 4. A method as in claim 1, each aperture having an inneraperture surface extending inwardly into the absorbent pad, includingside walls and a bottom of the respective aperture, the density of theabsorbent pad proximate the inner aperture surface being greater thanthe overall average density of the absorbent pad away from the aperture,each aperture defining an open cross-sectional area thereacross, the sumof the open cross-sectional areas of the apertures in said absorbent padcomprising about 5% to about 40% of the total surface area of the firstsurface.
 5. A method as in claim 4, each aperture having a diameter andspaced from a respective aperture in the longitudinal pattern a distanceapproximately equal to the diameter of the aperture so that the higherdensity and intermediate density zones, in combination, define saidliquid flow path for preferentially wicking and distributing theinsulting liquid along the pad in the longitudinal direction.
 6. Amethod as in claim 1, the longitudinal pattern of apertures definingmultiple liquid flow paths for preferential flow of the insulting liquidalong the absorbent pad, the liquid flow paths contributing toincreasing the distribution of the insulting liquid along the absorbentpad.
 7. A method as in claim 6, the absorbent pad having a length, thelongitudinal pattern of the apertures comprising a serpentine pattern,extending along the length of the absorbent pad.
 8. A method as in claim6, the absorbent pad having a length and a width, the longitudinalpattern of the apertures comprising four serpentine elements extendingalong the length of the absorbent pad, the respective serpentineelements being spaced from each other across the width of the absorbentpad.
 9. A method as in claim 6, each aperture having a diameter andspaced from a respective aperture in the longitudinal pattern a distanceapproximately equal to the diameter of the aperture so that the higherdensity and intermediate density zones, in combination, define saidliquid flow path for preferentially wicking and distributing theinsulting liquid along the pad in the longitudinal direction.
 10. Amethod as in claim 1, the higher and intermediate density zones,contributing to improved integrity of the absorbent pad.
 11. A method asin claim 1, each aperture having an inner aperture surface extendinginwardly into the absorbent pad, including side walls and a bottom ofthe respective aperture, the density of the absorbent pad proximate theinner aperture surface being greater than the overall average density ofthe absorbent pad, such that wicking of the insulting liquid developspreferentially around and among the apertures.
 12. A method as in claim1, the absorbent pad having a length and a width, the longitudinalpattern of the apertures comprising a relatively uniform array ofapertures along the length and width of said absorbent pad.
 13. A methodas in claim 1, the apertures having open cross-sections corresponding todiameters of about 0.25 inch.
 14. A method as in claim 1, the insultingaqueous liquid being preferentially wicked away from the liquid-insultedportion of the first surface along the liquid flow path defined amongthe longitudinal pattern of apertures.
 15. A method as in claim 1, saidapertures having bottoms including pillows of partially densifiedfibrous material in the bottoms of respective ones of said apertures.16. A method as in claim 1, the apertures having open cross-sectionscorresponding to diameters of greater than 0.109 inch.
 17. A method asin claim 1 wherein said apertures have depths of from about 40% to about99% of the thickness of said absorbent pad.
 18. A method as in claim 1wherein said apertures have depths of from about 50% to about 60% of thethickness of said absorbent pad.
 19. A method as in claim 1, furtherincluding preferentially drawing portions of the insulting liquidthrough said higher density zones and said intermediate density zonesfrom the second aperture toward the third aperture.
 20. A method as inclaim 1, the higher density and intermediate density zones, incombination, defining at least one liquid flow path for preferentiallywicking and distributing the insulting liquid along the pad in thelongitudinal direction.
 21. A method as in claim 1, the absorbent padhaving a length and the higher and intermediate density zones forming aliquid flow path for preferential flow of the insulting liquid along theabsorbent pad, the liquid flow path contributing to increasing thedistribution of the insulting liquid along the length of the absorbentpad relative to distribution of the insulting liquid transverse to thelength of the absorbent pad.
 22. A method as in claim 1, the absorbentpad having a liquid intake rate, the preferential wicking of theinsulting liquid along the liquid flow path drawing the insulting liquidaway from the apertures and thereby contributing to increasing theliquid intake rate of the absorbent pad at the apertures.